A high-bypass type turbofan engine generally includes a fan section and a core gas turbine engine. The gas turbine engine includes, in serial flow order, a low pressure compressor, a high pressure compressor, a combustion section, a high pressure turbine and a low pressure turbine. A high pressure shaft couples the high pressure compressor to the high pressure turbine. A low pressure shaft extends coaxially within the high pressure shaft and couples the low pressure compressor to the low pressure turbine.
The fan section includes a plurality of fan blades coupled to a fan shaft and disposed upstream from an inlet of the low pressure compressor. The fan shaft may be coupled to the low pressure shaft either directly or indirectly, for example, via a gearbox. In particular configurations, an outer casing or nacelle circumscribes the fan blades and at least a portion of the gas turbine engine. A bypass air passage is defined between an outer casing of the gas turbine engine and the nacelle.
In operation, air flows across the fan blades and towards the bypass air passage. A portion of the air flows into the inlet of the low pressure compressor while the remainder of the air is routed through the bypass passage. The air flowing though the inlet is progressively compressed as it flows through the low pressure compressor and the high pressure compressor, thus providing a highly compressed air to a diffuser cavity or head end portion of the combustion section. A portion of the compressed air flows into a combustion chamber of the combustion section. Fuel is injected into the combustion chamber via one or more fuel injectors. The fuel and air mixture is burned to provide combustion gases. The combustion gases are routed from the combustion chamber through the high pressure turbine, thus rotatably driving the high pressure compressor via the high pressure shaft. The combustion gases then flow aft through the low pressure turbine, thereby rotatably driving the low pressure compressor and the fan blades via the low pressure shaft and the fan shaft. The combustion gases are exhausted from the gas turbine via an exhaust nozzle, thus providing a portion of total thrust of the turbofan engine.
As the fuel-air mixture burns, pressure oscillations or “combustion dynamics”, driven at least in part by heat release during the combustion process, occur within the combustion chamber. These pressure oscillations generate acoustic waves that may propagate downstream from the combustion chamber towards the high pressure turbine and/or upstream from the combustion chamber back towards the diffuser cavity and/or the compressor outlet.
Low frequency to intermediate frequency combustion dynamics (50-250 Hz) such as those that occur during engine startup and/or during a low power to idle operating condition may negatively impact compressor stall margin, reduce operability margin of the turbofan engine and/or may increase external combustion noise or growl. In addition or in the alternative higher frequency combustion dynamics (250-1000 Hz) such as those that may occur during operation of the combustor may result in excitation of turbine blades or cause other vibration related issues. Consequently, a system for suppressing combustion dynamics within a combustion section of a gas turbine engine would be useful.